Acids don’t work as well on the substances that contribute to typical household drain clogs compared to bases, which is what Drano is.

When it enters your drain pipes, the sodium hydroxide reacts with fatty acids and proteins from your typical clogging culprits like oils, grease, soap scum, hair, and food particles.

This reaction generates heat, breaks large molecules into smaller ones, and liquefies solid gunk. The extremely high pH enables the sodium hydroxide to saponify fatsand dissolve organic matterthrough chemical decomposition.

Acids simply wouldn‘t have the same cleansing effects on drain clogs. Grease and oils are composed of tough-to-break-down fatty acid chains that resist acidic breakdown.

Quoted from here.